We propose to determine if the central effects of nicotine in rats is stereospecific. If so, we propose to make a systematic search in rat brain for stereospecific nicotine receptors, which may or may not be identical to the so-called nicotonic acetylcholine receptors. We will then characterize these receptors by their regional distribution in brain, and attempt to relate sites of high nicotine density to sites of nicotine action by local microinjection.